A developer wants to insert a record into an Amazon DynamoDB table as soon as a new file is added to an Amazon S3 bucket. Which set of steps would be necessary to achieve this?

The most efficient and direct method to meet this requirement is using an event-driven, serverless architecture. Amazon S3 event notifications can be configured to trigger an AWS Lambda function automatically and in near-real time when a specific event occurs, such as an object creation (s3:ObjectCreated:). The Lambda function receives the event data, which includes details about the new S3 object. The function's code can then use the AWS SDK to process this information and write a new record to the specified Amazon DynamoDB table. This pattern is highly scalable, cost-effective, and avoids the latency and inefficiency of polling.

A. Amazon EventBridge can react to S3 events, but it cannot directly insert records into DynamoDB. It would still require a target, such as a Lambda function, to perform the database write, making this option less direct than B.
C. Polling an S3 bucket with a Lambda function is an inefficient anti-pattern. It introduces latency, as the function only runs on a schedule, and incurs unnecessary costs from repeated API calls to list bucket contents.
D. A cron job is a scheduled task, not an event-driven one. This approach would introduce a delay between the file upload and the database insert, failing to meet the "as soon as" requirement.

1. AWS Lambda Developer Guide, "Using AWS Lambda with Amazon S3": This document explicitly describes the pattern of using S3 to trigger a Lambda function. It states, "You can use Lambda to process event notifications from Amazon Simple Storage Service. Amazon S3 can send an event to a Lambda function when an object is created or deleted in a bucket." (Section: "Tutorial: Using an Amazon S3 trigger to invoke a Lambda function").

2. Amazon S3 User Guide, "Amazon S3 event notifications": This guide details how to configure notifications and lists AWS Lambda as a primary destination. "Amazon S3 event notifications can be sent to the following destinations: Amazon Simple Notification Service (Amazon SNS) topics, Amazon Simple Queue Service (Amazon SQS) queues, and AWS Lambda functions." (Section: "Event notification destinations").

3. AWS Lambda Developer Guide, "Tutorial: Using an Amazon S3 trigger to create thumbnail images": This official tutorial provides a step-by-step implementation of a nearly identical pattern (S3 trigger -> Lambda -> S3 write), which demonstrates the core principle of S3 event notifications invoking a Lambda function for processing. The same logic applies to writing to DynamoDB instead of S3.